---

name: sql description: SQL and database best practices including query optimization, indexing, and schema design. globs: ["/*.sql", "/migrations/", "/prisma/", "/drizzle/**"] priority: 80 tags: ["database"]

SQL Best Practices

Query Writing

• Use parameterized queries (prevent SQL injection)
• Select only needed columns (avoid SELECT *)
• Use appropriate JOINs
• Add WHERE clauses to limit results
• Use EXPLAIN to analyze queries

Indexing

• Index columns used in WHERE/JOIN/ORDER BY
• Use composite indexes for multi-column queries
• Don't over-index (slows writes)
• Consider covering indexes
• Monitor index usage

Schema Design

• Use appropriate data types
• Add constraints (NOT NULL, UNIQUE, FK)
• Normalize to 3NF, denormalize for performance
• Use UUIDs for distributed systems
• Add created_at/updated_at columns

Transactions

• Keep transactions short
• Use appropriate isolation levels
• Handle deadlocks gracefully
• Use optimistic locking when appropriate

Migrations

• Make migrations reversible
• Test migrations on copy of prod data
• Use small, focused migrations
• Never modify existing migrations
• Back up before migrating

Performance

• Use connection pooling
• Implement pagination
• Cache frequent queries
• Use read replicas
• Monitor slow queries